Neuronal communication relies on the localization of specialized proteins to sites of synaptic transmission in both presynaptic and postsynaptic cells. Our research focus is on the characterization of PSD-95, an abundant protein found within the postsynaptic density, and its localization and function during development in dissociated hippocampal neuron cultures. Various GFP-fusion constructs will be used to study PSD-95 trafficking and localization in real time using confocal microscopy and then other synaptic proteins will be analyzed and their relative localization compared to PSD-95 using fusions containing variants of GFP and retrospective immunocytochemistry. The questions to be addressed are as follows: i) are there compensatory mechanisms between the MAGUK family of proteins that regulate their expression? ii) is PSD-95 a determinant factor in the process of synaptogenesis, or merely another protein recruited to the synapse? iii) does PSD-95 play a role in the synaptic targeting and localization of NMDA receptors? Real time analysis of these fundamental processes will significantly contribute to our understanding of synapse formation, a function required for organization of circuits throughout the entire nervous system.